Semiconductor devices typically include multiple patterned material layers in which each successive layer must be aligned to previous layers within tight tolerances. Accordingly, fabrication lines may utilize a process control system incorporating feedback and/or feedforward control data to monitor and adjust the settings of fabrication tools to maintain overlay errors (e.g., overlay registration errors between layers) within selected tolerances. Advanced process control systems providing tight overlay control typically integrate control data generated at multiple steps in the fabrication process from multiple types of equipment. For example, after development inspection (ADI) data may typically be generated using an optical metrology tool to provide high throughput analysis. By way of another example, after etch inspection (AEI) data may typically be provided by an electron-beam metrology tool to provide higher-resolution, but lower throughput analysis.
However, overlay errors measured at different stages of fabrication and/or by different metrology tools may differ. This difference between offset error measurements used as control data is termed non-zero offset (NZO) and may vary spatially across a particular sample and/or temporally across multiple samples in the same or different lots. In this regard, NZO may introduce instability into the process control system and may decrease performance. Therefore, it is desirable to develop systems and methods to cure deficiencies such as those identified above.